1. Field of the Invention
The present invention relates to a phase difference plate which is suitable for a reflection-type liquid crystal display device which can be used as a display device in various fields such as personal computers, AV equipment, portable information communication devices, game and simulation devices, on-board navigation systems, and the like, and to a norbornene based resin composition which is suitably used in the phase difference plate.
2. Description of the Related Art
A xcex/4 plate, whose retardation (Re) is xc2xc of the length of a wavelength, has various applications in reflection-type LCDs, pick-up for optical discs, anti-glare films, and the like. A xcex/2 plate, whose retardation (Re) is xc2xd of the length of a wavelength, is useful as a liquid crystal projector. In each of these applications, it is preferable that the xcex/4 plate and the xcex/2 plate sufficiently exhibit functions with respect to all of the incident light in the range of visible light which can be seen by the human eye.
For example, Japanese Patent Application Laid-Open (JP-A) Nos. 5-27118, 5-100114, 10-68816 and 10-90521 have proposed, as wide band phase difference plates functioning as xcex/4 plates and xcex/2 plates with respect to incident light in the entire visible light region, structures in which two polymer films having respective different optical anisotropy are layered.
However, in these cases, in the production thereof, it is necessary to obtain two types of chips in which elongate films, which are each drawn in one direction, are cut in directions forming different angles with respect to the directions of drawing, and to laminate these chips together. In such a xcex/4 plate, the optical anisotropy (inclination of the optical axis or the slow axis) of each polymer film is determined by the angle at which the chip is cut with respect to the direction of drawing of the drawn film. Thus, a precise cutting technology is required. Moreover, when the two chips are laminated, an adhesive must be applied and precise alignment must be carried out, such that the production processes are complex. Namely, processes such as an adhering process, a chip-forming process, a laminating process, and the like result in an increase in costs. Further, dirtying caused by the scum produced during chip-forming and the like, dispersion in the phase differences caused by errors in the laminating angle, and the like adversely affect the actual performances.
Currently, there has not yet been provided a technology in which a wide band xcex/4 plate or a wide band xcex/2 plate, which has retardation of xc2xc wavelength or xc2xd wavelength in the entire region of visible light and which is sufficiently durable to be able to withstand use, is formed by a single material without forming layers.
An object of the present invention is to provide a phase difference plate which can be formed by a single material at a low cost without having to form a laminated structure, and which exhibits excellent performances in a wide band. Moreover, an object of the present invention is to provide a norbornene based resin composition which is suitably used in the phase difference plate.
The norbornene based resin composition of the present invention comprises: a norbornene based resin; and a polymer whose birefringence value is negative, and whose wavelength dispersion of birefringence values satisfies |xcex94n(450)/xcex94n(550)|xe2x89xa71.02, wherein xcex94n(450) and xcex94n(550) are birefringence values (xcex94n) at a wavelength of 450 nm and a wavelength of 550 nm, respectively.
The phase difference plate of the present invention is formed by using the norbornene based resin composition of the present invention.